Crossroads of a Continent: Missouri Railroads, 1851-1921 tells the story of the state's railroads and their vital role in American history. Missouri and St. Louis, its largest city, are strategically located within the American Heartland. On July 4, 1851, when the Pacific Railroad of Missouri began construction in St. Louis, the city took its first step to becoming a major hub for railroads. By the 1920s, the state was crisscrossed with railways reaching toward all points of the compass.